1. Field
The disclosed concept relates to electrical switching apparatus and, more particularly, to circuit interrupters, such as, for example and without limitation, aircraft or aerospace circuit breakers including an electronic trip circuit, remote control circuit breakers, and remote power controllers.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
Subminiature circuit breakers are used, for example, in aircraft or aerospace electrical systems where they not only provide overcurrent protection but also serve as switches for turning equipment on and off. Such circuit breakers must be small to accommodate the high-density layout of circuit breaker panels, which make circuit breakers for numerous circuits accessible to a user. Aircraft electrical systems, for example, usually consist of hundreds of circuit breakers, each of which is used for a circuit protection function as well as a circuit disconnection function through a push-pull handle.
In many military applications, moisture resistance, vented and sealed units, and corrosion resistance are key attributes of modern aerospace circuit breakers, which seek to avoid failures resulting from arcing and/or dielectric breakdown. For example, if a molded circuit breaker case absorbs moisture or retains moisture from its molding process, then this could contribute to a premature product failure resulting from arcing and/or dielectric breakdown.
Military specification MIL-83383 for remote control circuit breakers (RCCBs) has dictated the use of thermoset compounds for the molded circuit breaker case.
U.S. Patent Application Publication No. 2009/0027154 discloses a circuit breaker including a trip indicator, which is preferably made of a suitable liquid crystal polymer (LCP), which provides suitable flexibility while also being suitably durable.
U.S. Pat. No. 7,170,376 discloses a circuit breaker housing and a trip circuit forming a composite structure. The housing halves are preferably made from liquid crystal polymer thermoplastic, which may be molded to provide relatively very thin walls (e.g., without limitation, less than about 0.010 in. (about 0.254 mm)) with an irregular wall thickness and a relatively complex geometry, thereby providing superior strength and temperature insulation characteristics. The housing halves also electrically and thermally insulate the arc fault detector (AFD) printed circuit board (PCB) electronics from the current carrying operating mechanism. Over-molding of the AFD PCB electronics provides structural and overall package integrity as may be employed, for example, for aerospace use. The PCBs are made of an FR4 electronics substrate having a thickness of about 0.018 inch.
Vance, Jr., J., “Insert Molding”, Medical Device & Diagnostic Industry Magazine, April 1996, pp. 1-2, discloses that insert molding is an injection molding process whereby plastic is injected into a cavity and around an insert piece placed into the same cavity just prior to molding. The result is a single piece with the insert encapsulated by the plastic. The insert can be made of metal or another plastic. The technique was initially developed to place threaded inserts in molded parts and to encapsulate the wire-plug connection on electrical cords. There are two types of bonding that occur in insert molding, molecular and mechanical. Molecular bonding can occur when the insert material is the same as or similar to the encapsulating resin. This will yield the best results from the joint, both for physical strength and leak resistance. An example would be molding a polyurethane bifurcation to a polyurethane catheter. Mechanical bonding can take place in two ways, by the shrinking of the encapsulating resin around the insert as the resin cools, or by the surrounding of irregularities in the surface of the insert by the encapsulating resin. Although shrinkage always occurs, it is rarely sufficient to produce adequate physical strength or leak resistance of the joint. In general, when insert molding dissimilar materials, the insert should offer some means of mechanical retention such as a sandblasted, flared, or knurled surface.
Insert molding is also known as a process in which plastic is injected into a mold that contains an pre-placed insert. The result of insert molding is a single molded plastic piece with an insert surrounded by the plastic. Inserts can be made of metals or different types of plastic. Insert molding is used in many industries. Applications of insert molding include insert-molded couplings, threaded fasteners, filters, and electrical components.
There is room for improvement in circuit interrupters.